Synthesis of new unsymmetrical diamine and polyimides: structure–property relationship and applications of polyimides

A novel unsymmetrical diamine monomer 4-(2-(4-(4-aminophenoxy)phenyl)propan-2-yl)benzenamine (APPBA) containing –O– and –C(CH₃)– groups was synthesized from 2-(4-aminophenyl)-2-(4-hydroxyphenyl)propane and 4-nitrofluorobenzene by the nucleophilic substitution reaction followed by catalytic reduction. Polycondensation of this diamine with aromatic dianhydrides through thermal solution imidization techniques afford a series of novel processable polyimides (PI). The structure of the monomer and polyimides were confirmed by FT-IR and ¹H-NMR. The polyimides were characterized by XRD, TGA, DSC, electrical property, solution viscosity and solubility test. These polyimides had inherent viscosities in the range 0.48–0.61 dL/g. The X-ray diffraction measurements indicated that all these polyimides were amorphous. The polyimides exhibited excellent solubility in most of the organic solvents. The glass transition temperature (Tg) was observed in the range 242–282 °C. The polyimides displayed good thermal stability and the temperatures at which 10 % weight loss occurred in the range 475–504 °C. The dielectric constant of PIs was in the range of 2.82–3.55.